1. Field of the Invention
This invention relates to a vaporized fuel control system for a vehicular internal combustion engine enabling to use a blended fuel of gasoline and alcohol.
2. Description of the Prior Art
As a vaporized fuel control system for an engine able to use a blended fuel composed of gasoline and an alcohol such as methanol (methyl alcohol), Japanese Laid-open Patent Publication No. 1-106,971 teaches a system characterized in that the amount of the vaporized fuel supplied to the engine air intake system is controlled in proportion to the alcohol concentration of the fuel.
Apart from the above, recent years have seen an increasing number of proposals to reduce the size and weight of various components mounted on or connected to a vehicular internal combustion engine in order to improve fuel consumption efficiency. A fuel tank will be one of the components to be made smaller and lighter. However, when a fuel tank contains the blended fuel composed of gasoline and an alcohol such as methanol, the reid pressure of the vaporized fuel in the tank varies with respect to its methanol content as shown in a graph of FIG. 4. The reid vapor pressure, often called "RVP" in the field, has a close relationship with the pressure in the tank. In order to reduce the size and weight of the fuel tank, the pressure in the tank should be, therefore, regulated at a predetermined level.
The object of this invention is therefore to provide a system for controlling the amount of vaporized fuel in a fuel tank composed of a blend of gasoline and an alcohol such as methanol in which the pressure in the fuel tank is regulated properly so as to make it possible to reduce the size and weight of the fuel tank and thus improve fuel consumption efficiency.